Channel estimation apparatus and method for the same

1. A channel estimation apparatus, comprising: a preamble buffer unit, adapted for receiving and storing a plurality of symbols of a preamble signal, the symbols corresponding to a plurality of gain control values; a gain adjustment unit, adapted for adjusting the symbols to a plurality of gain normalized symbols according to the gain control values; a demodulation unit, adapted for receiving and demodulating the gain normalized symbols to obtain a frequency domain demodulation signal; an estimation unit, receiving the frequency domain demodulation signal, and multiplying the frequency domain demodulation signal with a conjugate value of a frequency domain reference value of a standard preamble signal to obtain a frequency response of a channel; and a multiplexing control unit, coupled to the preamble buffer unit and the gain adjustment unit, and adapted for outputting a control signal for controlling the preamble buffer unit and the gain adjustment unit.

2. The channel estimation apparatus according to claim 1 , wherein each of the symbols comprises M sampling signals, and the preamble buffer unit comprises: a plurality of sampling registers, for storing M sampling signals of the symbols respectively; and a first multiplexer, for receiving the symbols of the preamble signal, and determining whether to output the symbols to the sampling registers according to the control signal, wherein M is a natural number.

3. The channel estimation apparatus according to claim 2 , wherein the gain adjustment unit comprises: a gain storing unit, for storing the gain control values corresponding to the symbols; a second multiplexer, for determining whether to read out the gain control values stored in the gain storing unit according to the control signal; a calculation unit, coupled to the second multiplexer, for comparing the gain control value with a reference gain control value, and outputting a plurality of gain adjustment ratios corresponding to the symbols; a third multiplexer, for determining whether to read out the symbols stored in the sampling registers according to the control signal; and a first multiplication unit, coupled to the third multiplexer and the calculation unit, for multiplying M sampling signal with the gain adjustment ratios corresponding to the symbols, so as to output the gain normalized symbols, wherein the gain normalized symbols comprise M gain normalized sampling signals.

4. The channel estimation apparatus according to claim 3 , wherein the calculation unit comprises: an addition unit, coupled to the second multiplexer, for subtracting the gain control values respectively with the reference gain control values, and outputting a plurality of gain difference values; and a gain mapping table, for detecting the gain adjustment ratios according to the gain difference values.

5. The channel estimation apparatus according to claim 4 , wherein the gain adjustment unit further comprises: an output saturation indication unit, for receiving and recording a plurality of output saturation indexes corresponding to the symbols.

6. The channel estimation apparatus according to claim 5 , wherein the output saturation indication unit comprises: an output saturation recorder, for receiving and storing the output saturation indexes corresponding to the symbols; and a fourth multiplexer, for reading out the output saturation indexes stored in the output saturation recorder to the gain mapping table, wherein the output saturation indexes correspond to the gain adjustment ratios of the symbols, and if a specific one of the output saturation indexes is true, the gain mapping table sets a specific one of the gain adjusting ratios corresponding to the specific one output saturation index as 0.

7. The channel estimation apparatus according to claim 6 , wherein the gain adjustment unit further comprises: an averaging unit, coupled to the first multiplication unit and the output saturation recorder, for determining number of the output saturation indexes which are true, and generating an adjustment parameter for performing a parameter adjustment calculation to the gain normalized symbols.

8. The channel estimation apparatus according to claim 7 , wherein the averaging unit comprises: a parameter generator, for determining number of the output saturation indexes which are true, and generating an adjustment parameter according to the quantity; and a second multiplication unit, for multiplying the M gain normalized sampling signals of the gain normalized symbols with the adjustment parameter.

9. The channel estimation apparatus according to claim 7 , wherein the demodulation unit comprises: a plurality of input buffers, for respectively storing the M gain normalized sampling signals of the gain normalized symbols, wherein the input buffers comprise M×L signal samples, in which L is a natural number; a fifth multiplexer, for outputting the M gain normalized sampling signals of the gain normalized symbols to the input buffers according to and timing offset of the symbols; and a fast Fourier transform (FFT) unit, capable of M×L points of FFT calculation, for performing an M×L points of FFT calculation with the M gain normalized sampling signal of the gain normalized symbols stored in the input buffers, so as to output the frequency domain demodulation signal, wherein the frequency domain demodulation signal comprises M×L frequency domain components.

10. The channel estimation apparatus according to claim 9 , wherein the estimation unit comprising: an extraction unit, for picking up one frequency domain sampling signal from each L frequency domain components in sequence so as for obtaining M frequency domain sampling signals from M×L frequency domain components; and a third multiplication unit, coupled to the extraction unit, for multiplying the M frequency domain sampling signals with a frequency domain reference value corresponding to the standard preamble signal, so as to obtain an estimated frequency response.

11. A method for channel estimation, comprising: receiving a plurality of symbols of a preamble signal, wherein the symbols correspond to a plurality of gain control values; adjusting the symbols to a plurality of gain normalized symbols according to the gain control values; demodulating the gain normalized symbols and obtaining a frequency domain demodulation signal; multiplying the frequency domain demodulation signal with a conjugate value of a frequency domain reference value of a standard preamble signal, so as to obtain a frequency response of a channel; subtracting the gain control values with a reference gain control value respectively, and outputting a plurality of gain difference values; detecting a plurality of gain adjustment ratios according to the gain difference values; and multiplying M sampling signals of the symbols with the gain adjustment ratios corresponding to the symbols, so as to output the gain normalized symbols, each of which comprising M gain normalized sampling signals, wherein M is a natural number.

12. The method for channel estimation according to claim 11 further comprising: receiving a plurality of output saturation indexes; and if a specific one of the output saturation indexes is true, then setting a gain adjustment ratio corresponding to the specific output saturation index as 0.

13. The method for channel estimation according to claim 12 further comprising: determining an adjustment parameter according to number of output saturation indexes which are true; and multiplying the M gain normalized sampling signals of the gain normalized symbols with the adjustment parameter.

14. The method for channel estimation according to claim 13 , wherein the step of demodulating the gain normalized symbols and obtaining a frequency domain demodulation signal comprises: performing an M×L points of fast Fourier transform (FFT) on the M gain normalized sampling signal of the gain normalized symbols, to obtain the frequency domain demodulation signal by the FFT output, wherein the frequency domain demodulation signal comprises M×L frequency domain components and L is a natural number.

15. The method for channel estimation according to claim 14 further comprising: picking up one frequency domain component from each L frequency domain components in sequence, so as to obtain M frequency domain sampling signals from M×L frequency domain components; and multiplying the M frequency domain sampling signals with a frequency domain reference value corresponding to the standard preamble signal, so as to obtain an estimated frequency response of the channel.